Structure of operational amplifier

ABSTRACT

An operational amplifier including a differential amplifier circuit, and a reverse output buffer. The reverse output buffer has a first forward switch, a second forward switch, a first reverse switch, and a second reverse switch. The first forward switch and the first reverse switch and the second forward switch are connected in series between a reference voltage source and a grounding terminal. The second forward switch being connected between the output terminal of the operational amplifier and the grounding terminal. The second reverse switch and the second forward switch are electrically connected by a bias voltage provided from a bias voltage input terminal connected thereto, so that when the second bias voltage input terminal is at low potential and the first bias voltage is at high potential, the second reverse switch is on, and the second forward switch is off. The operational amplifier will then function normally. When the second bias voltage input terminal is at high potential and the first bias voltage input terminal is at low potential, the second reverse switch is off, and the second forward switch is on. This causes the operational amplifier to consume no electricity, and the output terminal to provide a stable low voltage output.

BACKGROUND OF THE INVENTION

The present invention related to operational amplifiers, and moreparticularly to an improved amplifier structure which consumes noelectric current and provides a stable output when not working.

Following rapid development of integrated circuit technology, advancedICs, such as micro-controllers, digital-to-analog converters, memorydevices, and etc., are made having a minimized dimension withsophisticated operation capability. Operational amplifiers are used in avariety of IC chips. FIG. 1 illustrates a conventional operationalamplifier. This amplifier structure is composed of CMOS (complementarymetal-oxide semiconductor) comprising a differential amplifier 10, areverse output buffer 20, a non-inverting terminal IP, an invertingterminal IN, a bias voltage input terminal AVB, and an output terminalOI. The differential amplifier 10 is composed of semiconductor switchesM1˜M5, and is connected to the non-inverting terminal IP and theinverting terminal IN. The reverse output buffer 20 is comprised of twosemiconductor switches, namely, the reverse switch M6 and the forwardswitch M7 connected between a reference voltage and a grounding terminalGND. The output terminal O1 is connected between the semiconductorswitches M6 and M7 of the reverse output buffer 20. An input biasvoltage signal is provided through the bias voltage input buffer 20 toelectrically connect the forward switch M7, so as to achieveproportional output. This structure of this operational amplifier iscommonly used in mobile electronic apparatus such as mobile telephones,notebook computers, and personal digital assistant. However, thisamplifier structure is not satisfactory because it consumes to muchelectric current when not working.

SUMMARY OF THE INVENTION

It is the main object of the present invention to provide an operationalamplifier, which consumes no power AND provides a stable output signalthrough its output terminal when it is not working. The reverse outputbuffer according to the present invention comprises a second reverseswitch and a second forward switch. The second reverse switch isconnected is connected in series between the first reverse switch andthe reference voltage. The second forward switch is connected isconnected between the output terminal and the grounding terminal GND. Abias voltage provided from a second bias voltage input terminal of theoperational amplifier electrically connects the second reverse switchand the second forward switch. When the second bias voltage inputterminal is at low potential and the first bias voltage input terminalis at high potential, the second reverse is on, and the second forwardswitch is off, thereby causing the operational amplifier to functionnormally. When the s second bias voltage input terminal is at highpotential and first bias voltage input terminal is at low potential, thesecond reverse switch is off, and the second forward switch is on,thereby causing the operation amplifier to consume no electricity, andthe output terminal to provide a stable low voltage output.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of an operational amplifier according to theprior art.

FIG. 2 is a circuit diagram of an operational amplifier according to thepresent invention.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 2, an operational amplifier in accordance with thepresent invention is comprise of a differential amplifier circuit 10, areverse output buffer 20, a non-inverting terminal IP, an inverting afirst bias voltage input terminal IN, a first bias voltage inputterminal AVB, a second bias voltage input terminal AVB1, and an outputterminal 01. The differential amplifier 10 is composed of semiconductorswitches M1˜M5, and is connected to the non-inverting terminal IP, theinverting terminal IN and the first bias voltage input terminal AVB. Thereverse output buffer 20 comprises a first reverse switch M6, a firstforward switch M87, a second reverse switch M9, and a second forwardswitch M8. The first forward switch M87, the first reverse switch M6 andthe second reverse switch M9 are connected in series between a groundingterminal GND and a reference voltage. The output terminal 01 isconnected between the semiconductor switches M6 and M7 of the reversebuffer 20. The first bias voltage input terminal AVB provides a biasvoltage to the differential amplifier 10 and to the reverse outputbuffer 20 which are electrically connected to the first forward switchM7 of the reverse output buffer 20. The second bias voltage inputterminal AVB1 provides a bias voltage to electrically connect the secondreverse switch M9 and the second forward switch M8. The second reverseswitch M9 is connected in series between the reference voltage and thefirst reverse switch M6. The second forward switch M8 is connectedbetween the output terminal 01 and the grounding terminal GND.

Referring to FIG. 2 again, when the second bias voltage input terminalAVB 1 is at a low potential Lo and the first voltage input terminal AVBis at a high potential Hi, the second reverse switch M9 is on, and thesecond forward switch M8 is off, and therefore the operation amplifierfunctions normally. When the second bias voltage input terminal AVB1 isat high potential Hi and the first bias voltage input terminal AVB is atlow potential Lo, the second reverse switch M9 is off, and the secondforward switch M8 is on, and therefore the operation amplifier does notwork. At this stage, the reverse output buffer 20 consumes no electriccurrent (because the second reverse switch M9 is off, and the outputterminal 01 provides a stable low voltage output (because the secondforward switch M8 is on).

As indicated above, the added second forward switch M8, second reverseswitch M9 and second bias voltage input terminal AVB1 enable the reverseoutput buffer 20 to consume no electric current and the output terminal01 to provide a stable low voltage output when the operation amplifieris not working.

While only embodiment of the present invention has been shown anddescribed, it will be understood that various modifications and changescould be made thereunto without departing from the spirit and scope ofthe invention disclosed.

What the invention claimed is:
 1. An operational amplifier comprising adifferential amplifier circuit, a reverse output buffer, a non-invertingterminal, an inverting terminal, a first bias voltage input terminal,and an output terminal, said differential amplifier comprising aplurality of semiconductor switches and being connected to saidnon-inverting terminal, said inverting terminal and said first biasvoltage input terminal; said reverse output buffer comprising a firstreverse switch and a first forward switch connected in series between areference voltage and a grounding terminal, said output terminal beingconnected between said first reverse switch and said first forwardswitch, said first bias voltage input terminal being controlled toprovide a bias voltage to said differential amplifier and said reverseoutput buffer to electrically connect said connect said first forwardswitch of said reverse output buffer; said reverse output buffer furthercomprising a second reverse switch connected in series between saidreference voltage and said first reverse switch, and a second forwardswitch connected between said output terminal and said groundingterminal, said second reverse switch and said second forward switchbeing electrically connected by a bias voltage provided from a secondbias voltage input terminal connected thereto so that when said secondbias voltage input terminal is at low potential and said first biasvoltage input terminal is at high potential, said second reverse switchis on, and said second forward switch is off, said operational amplifierwill function; and when said second bias voltage input terminal is athigh potential and said first bias voltage input terminal is at lowpotential, said second reverse switch is off, and said second forwardswitch is on, said operational amplifier will not work and will consumeno electric current, and said output terminal providing a low potentialoutput.